Prince was rushed to a hospital early Friday morning after his jet made an emergency landing in Illinois … TMZ has learned.

According to our sources, Prince’s private plane made an unscheduled landing at Quad City International Airport in Moline just after 1 AM. The singer was immediately transported by ambulance to a nearby hospital.

One source tells TMZ Prince is still in the hospital and “not doing well,” however another source close to the 57-year-old singer tells us he’s been released and is doing okay. The nature of the medical emergency is unclear.

The Rock and Roll Hall of Famer had performed Thursday night in Atlanta … and he was in the air for only a short time before things went south.